SkTypeface to use SkStreamAsset.

SkTypeface already requires typeface streams to support SkStreamAsset
in practice, and in practice all users are already supplying them.

Review URL: https://codereview.chromium.org/869763002
diff --git a/src/ports/SkTypeface_win_dw.cpp b/src/ports/SkTypeface_win_dw.cpp
index b777806..eb17201 100644
--- a/src/ports/SkTypeface_win_dw.cpp
+++ b/src/ports/SkTypeface_win_dw.cpp
@@ -209,7 +209,7 @@
     return size;
 }
 
-SkStream* DWriteFontTypeface::onOpenStream(int* ttcIndex) const {
+SkStreamAsset* DWriteFontTypeface::onOpenStream(int* ttcIndex) const {
     *ttcIndex = fDWriteFontFace->GetIndex();
 
     UINT32 numFiles;